1. Field of the Invention
This invention relates to an apparatus for optically generating chaotic random numbers.
2. Description of Related Art
Certain applications require a truly random number to be generated. Such applications include encryption, identification, access control and audio (to generate noise). Random number generating circuits for generating random numbers are well known. The most common of these circuits are based on the noise property of a biased semiconductor device or other circuit components. Some circuits use oscillators and rely on the natural variation in the frequency of slow oscillators to control the sampling of faster oscillators.
One difficulty in generating a random number using noise is the fact that an integrated circuit, whether analog or digital, is essentially designed to be deterministic in nature; for a given set of inputs, there will be a given set of outputs. The one parameter of integrated circuits that is truly random is the thermal noise. However, since the thermal noise constitutes a relatively small signal, it must be amplified to be utilized as a random noise source. However, this presents some difficulty in that any on-chip amplifier is subject to interference from other portions of the circuit, i.e., interference through the power supply or the substrate. This interference, as compared to the thermal noise, is not random. The interference is primarily determined by the operation of other parts of the circuits. It can either be periodic, if it is generated from a clock circuit, or it can be data dependent, if it is generated from data processing circuitry. Thus, conventional digital circuits which utilize noise to generate random numbers are somewhat deterministic, resulting in the output of a conventional digital circuit to be predictable in nature. However, the output of a random number generator should be truly random rather than deterministic. This feature makes conventional random number generators difficult to design, build, and test using standard digital circuitry techniques. Accordingly, what is needed is a system and method for generating random numbers in a chaotic and non-deterministic manner.
The present invention provides a system and method for optically generating random numbers in a chaotic manner. The optical random number generator includes an optical interferometer having a chaotic output which is dependent upon temperature fluctuations in its surrounding micro-environment. The interferometer receives light from a light source, splits the received light between a pair of temperature-sensitive optical paths, and interferes the split light traveling on the pair of optical paths to generate an output signal. The power of the interferometer output signal is measured and compared with a threshold value in order to generate a random number based on the measured interferometer output power.
The optical random number generator assigns a random number based on the relationship between the measured interferometer output power and the threshold value. The half power point of the interferometer output power is preferably initially selected as the threshold value, since the interferometer output power response will fluctuate sinusoidally about the half power point with changes in phase shift. The interferometer phase shift will change with temperature fluctuations in the surrounding micro-environment which causes the interferometer output power to fluctuate accordingly. Thus, the resulting generated random numbers will also change along with these temperature fluctuations and will not be predictable in practice. The threshold value may also be monitored and altered as a moving average of recent interferometer output power measurements in order to maintain a threshold value having a substantially equal chance of being either above or below the measured interferometer output power.
Chaotic behavior in the interferometer output power is achieved by making the interferometer phase shift extremely sensitive to temperature fluctuations, where small changes in the temperature of the interferometer micro-environment will alter the output power of the interferometer. Temperature sensitivity of the phase shift in the interferometer is achieved utilizing a pair of optical paths having different lengths. The lengths of the optical paths are selected to achieve the desired temperature sensitivity. Alternatively, temperature sensitivity can be achieved through the use of pyroelectric material in the interferometer for generating electric fields which act on the light traveling through the optical paths in response to temperature fluctuations.